In connection with open-heart surgery, it is common to "harvest" a vein from the leg of the patient for use in a graft during the surgical process. Once the vein is removed from the patient, it must be distended by the introduction of a fluid, usually blood, to check the integrity of the vein as to leaks or other characteristics. In this process, it is very important that the testing be accomplished without overly distending the vein. A maximum pressure of 250 millimeters of mercury is desirable.
Excessive distention pressures during vein testing are known to affect adversely the endothelial covering and instigate progressively degenerative and regenerative changes throughout the layers, thus predisposing to early graft thrombosis or subintimal hyperplasia.
The testing is done by using a syringe which is filled with a predetermined quantity of blood and then a cannula connected to the syringe is inserted into one end of the vein and the other end is closed for the testing.
Other uses include the administration of local anesthetic to a tourniquetted area to prevent excusion beyond the desired area, and the inflation of balloon cuffs on a variety of cannulae and catheters.
It is an object of this invention to provide a syringe which can be manufactured to specific pressure limits and which has a tactile feedback to alert the surgeon when a certain pressure has been reached.
It is a further object to provide a distending syringe which is relatively inexpensive and which can be furnished in sterile condition and disposed of when the particular use is completed.
It is a further object to provide a syringe which can be manipulated with one hand and which signals the surgeon when a certain pressure is reached.
It is known to attach a stationary pressure gauge between the syringe and a cannula to monitor the pressure in the vessel as described in the Annals of Thoracic Surgery, Vol. 41, No. 5, May 1986, Page 569. Another vein distention system utilizes a balloon on the syringe to control the pressure in the vein (Bonchek-Shiley Vein Distentive System).
In the present invention a syringe plunger incorporates a spring-biased piston which is responsive to cannula pressure and which carries a stem projecting through the exterior plunger. The stem responds to movement of the piston and moves in contact with the surgeon's thumb to alert him to the set pressure limit.
Other objects and features of the invention will be set forth in the following description and claims in which the principles of the invention are set forth together with details to enable persons skilled in the art to practice the invention, all in connection with the best mode presently contemplated for the invention.